Effect of Microstructure on Corrosion Behavior of Alloy 800H in Supercritical Water
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摘要: 800H合金在超临界水冷堆的设计中被列为主要候选核燃料包壳材料之一，但是其在应用工况下的腐蚀性能受到加工状态的显著影响。本文通过高压釜浸泡试验、微观表征和机理分析对不同状态的800H合金在超临界水中的腐蚀行为进行研究，获得了表面磨抛状态、冷变形量和晶粒度对其均匀腐蚀行为的影响规律。结果表明：表面粗磨、冷变形和晶粒细化均可显著降低腐蚀速率，引起腐蚀增重规律由抛物线型向直线型转变；晶粒细化提高了材料的晶界密度，Cr在晶界附近的快速扩散有利于Cr2O3保护层的形成，可提高材料的耐腐蚀性能；表面粗磨后留下的浅表面变形层可在高温下再结晶形成高密度的纳米晶，这有利于表面Cr2O3保护层的快速形成，对初期腐蚀行为的抑制作用显著；轧制形成的冷变形提高了材料整体的晶界和位错密度，对包壳管的长期抗腐蚀能力具有明显的提升作用。Abstract: Alloy 800H is listed as one of the main candidate nuclear fuel cladding materials in the design of supercritical water-cooled reactor (SCWR), but its corrosion performance under application conditions is significantly affected by processing conditions. In this paper, the corrosion behavior of Alloy 800H in different states in supercritical water is studied by autoclave immersion test, microscopic characterization and mechanism analysis, and the effects of surface grinding and polishing state, cold deformation and grain size on its general corrosion behavior are obtained. The results show that surface rough grinding, cold deformation and grain refinement can significantly reduce the corrosion rate and cause the law of corrosion weight gain to change from parabolic to linear. Grain refinement improves the grain boundary density of the material, and the high diffusion rate of Cr near the grain boundary is conducive to the formation of the Cr2O3 protective layer, thus improving the corrosion resistance of the material. The shallow surface deformation layer left after surface rough grinding can be recrystallized into high-density nanocrystals at high temperature, which is conducive to the rapid formation of the surface Cr2O3 protective layer and has a significant inhibitory effect on the initial corrosion behavior. The cold deformation caused by rolling improves the grain boundary and dislocation density of material, which obviously enhances the long-term corrosion resistance of the cladding tube.
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Key words:
- SCWR /
- Alloy 800H /
- General corrosion /
- Cold deformation /
- Grain size /
- Surface state
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图 1 磨抛与轧制示意图 mm
TD—轧制横向；RD—轧制方向；ND—下轧方向
Figure 1. Schematic Diagram of Rolling, Grounding and Polishing Process
图 2 粗磨样品和抛光样品随浸泡时间的腐蚀增重曲线
Figure 2. Corrosion Weight Gain Curves of Ground and Polished Samples
图 3 粗磨样品和抛光样品腐蚀后的表面氧化物形貌
Figure 3. Surface Oxide Morphology of Ground and Polished Samples after Corrosion
图 4 抛光样品腐蚀1000 h后的截面形貌和元素分布
Figure 4. Cross Section Morphology and Element Distribution of Polished Samples after 1000 h Corrosion
图 5 粗磨样品腐蚀1000 h后的截面形貌、元素分布及线扫结果
Figure 5. Cross Section Morphology, Element Distribution and Line Scan Result of Polished Samples after 1000 h Corrosion
图 6 不同表面磨抛状态样品的ρGND分布
Figure 6. ρGND Distribution of Samples with Different Surface States
图 7 不同冷变形量抛光样品的腐蚀增重曲线
Figure 7. Corrosion Weight Gain Curves of Samples with Different Cold Deformation
图 8 80%冷变形量抛光样品腐蚀1000 h后的截面形貌、元素分布及线扫结果
Figure 8. Cross Section Morphology, Element Distribution and Line Scan Result of Polished Samples with 80% Cold Deformation after 1000 h Corrosion
图 9 不同晶粒度样品的腐蚀增重曲线
Figure 9. Corrosion Weight Gain Curves of Samples with Different Grain Sizes
图 10 粗晶样品和细晶样品的腐蚀表面形貌
Figure 10. Corrosion Surface Morphology of Coarse and Fine Crystal Samples
图 11 不同晶粒度样品的腐蚀截面形貌
Figure 11. Cross Section Morphology of Samples with Different Grain Sizes after Corrosion
图 12 不同晶粒度样品腐蚀表面的XRD图谱
F—基体；H—Fe2O3/ Cr2O3；M—Fe3O4/ FeCr2O4
Figure 12. XRD Spectrum of Samples with Different Grain Sizes after Corrosion
表 1 不同冷变形量抛光样品的腐蚀增重规律
Table 1. Corrosion Weight Gain Pattern of Samples with Different Cold Deformation
冷轧变形量/% $ k $ n $ R^{2} $ 0 12.56 0.469 0.995 20 15.54 0.423 0.986 40 19.57 0.281 0.993 60 17.32 0.176 0.993 80 17.94 0.088 0.889 
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